1. Field of the Invention
The present invention relates to firearms and in particular to a rifle which may be alternately operated in manual bolt action mode and semiautomatic or automatic mode.
2. Description of Related Art
Optimum center fire cartridge accuracy design requires a tight breech condition in that when the bolt face is locked in battery the bolt face cannot move rearward upon ignition, thereby supporting the shoulder of the cartridge and insuring contact of the cartridge shoulder to the chamber supporting the centrality of the neck of the case at time of ignition. The slightest rearward movement (or loss of headspace) of the cartridge away from the chamber neck wall can result in off center ignition allowing the projectile to offload on its imprint into the rifling of the barrel. The resultant off-center ignition and projectile seating will cause loss of accuracy at distance. Precision bolt action rifles do not have this concern because the bolt face is locked in head space. On the other hand gas-operated semiautomatic and automatic operating systems do exhibit rearward movement of the bolt face and breech lock at time of ignition to some degree, having potential for sloppier projectile seating into the rifling of the barrel causing a lower attainable MOA or accuracy at test. This is evident in some test criteria between M16 type rifles such as the SAS110 and M40 type bolt guns. This does not degrade either weapon type; it merely is a difference between the types that has impact on achievable targets at long range. The resultant practice is that most military field both a gas gun for semi-auto volume fire and a bolt gun for precision long range fire.
Current fielded platoon and scout/sniper weapon platforms include the M4 assault weapon the M40 or M24 precision bolt action rifle and also the SAS110 semi auto sniper for volume fire. These are distinct weapons with separate missions, i.e., close quarters fire, mid range fire, and/or precision long range fire.